1) What if the land is dryad arbor? Creatures can't enter the battlefield from graveyards
2) Also, what if I goblin weld my cage out for a creature? will the creature come back or is the cage still technically on the field during the weld?
3) Also, what if i have a goblin welder out, a cage on the field, and my opponent has a mox on the field and an artifact creature in the yard? can I weld out the mox for the illegal creature target, and use welder like a vindicate, or can you not weld because there's no legal target?
1. Can't be played from graveyard or fetched either.
2. Won't come back due to the 'simultaneously' on the oracle of welder.
3. Yes, this will work. Your opp will sacrifice the the mox and simultaneously bring the creature into play. This can't happen so the creature stays put.